Path: utzoo!attcan!uunet!lll-winken!ncis.llnl.gov!helios.ee.lbl.gov!nosc!manta!gutman
From: gutman@manta.NOSC.MIL (Lewis M. Gutman)
Newsgroups: comp.protocols.iso
Subject: Transport Protocol Downward Multiplexing
Keywords: Transport Protocol, Multiplexing
Message-ID: <432@manta.NOSC.MIL>
Date: 24 Jan 89 23:05:06 GMT
Organization: Naval Ocean Systems Center, San Diego
Lines: 49

We're designing a small internet, and in the process, have discovered a
problem we don't know how to resolve.  We are trying to adhere to the
OSI Reference Model as much as possible.

We have access to multiple networks with widely differing
characteristics, e.g., some are very slow but with low error rates,
others are faster but have higher error rates.  According to ISO 8073,
TP4 would be used for Type C Networks (those with unacceptable residual
error rates), and TP0 would be used for Type A Networks (those with
acceptable residual error rate).  ISO 8073 also specifies the use of
downward multiplexing of a single transport connection over multiple
network connections.  

We want to multiplex a single transport connection over multiple
network connections of different types, i.e., some Type A and some Type
C.   We're doing this in order to (1) guarantee delivery (multiple
copies), (2) increase throughput, and (3) send multicast messages to
destinations accessible only on several different networks.  


			Net 1 (75 bps, low BER)
            NSAP1  *-------------------
		  /
		 /
   SSAP	*-------* TSAP
		 \
		  \
            NSAP2  *-------------------
			Net 2 (2400 bps, high BER)


Because of the high overhead, we would like to avoid using TP4 over the
Net 1.   For this reason, the solution of using TP4 over all networks
is not necessarily acceptable.  Yet using TP0 over both nets is not
very good either: we need error recovery services for Net 2.  What can
we do?

Is it feasible to even consider this problem?  Do the standards say
anything about this kind of multiplexing?  Does anyone have any
experience multiplexing a single TP connection over network connections
of varying quality?  How is it done?

Thanks in advance.

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Lew Gutman					Naval Ocean Systems Center
E-Mail:  gutman@manta.nosc.mil			Code 854
Phone:   (619) 553-4958				San Diego, Ca. 92152
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